The broad objective of this research is to elucidate some of the variables which determine the degree of functional restitution after trauma to the mammalian spinal cord. The present experiments will utilize an aspect of functional spinal cord plasticity termed the "crossed phrenic phenomenon" to determine if the beneficial effects of this plasticity can be combined with other procedures to augment the degree of functional recovery of the respiratory diaphragm after spinal cord injury. After cervical hemisection of the spinal cord, the ipsilateral hemidiaphragm becomes paralyzed. This hemidiaphragm recovers, however, in several mammalian species if the contralateral phrenic nerve is transected. Although the phrenicotomy paralyzes the denervated hemidiaphragm, it activates a latent, crossed medullopsinal pathway (crossed phrenic pathway) which restores function to the opposite hemidiaphragm paralyzed by spinal cord injury. The purpose of the research is to determine if recovery can be achieved in the entire diaphragm after spinal cord injury. Electromyographic recordings from the diaphragm will be utilized to determine if repeated use of synapses in the crossed pathway for a few hours to several months will allow these synapses to operate after function is restored to the interrupted phrenic nerve. The contralateral phrenic nerve will be temporarily interrupted after hemisection by anesthetics, crush, or by transection with nerve grafting. The present experiments will also determine if functional recovery in both hemidiaphragms can be achieved by transecting the dorsal roots of the phrenic nerve opposite the hemisection. Since some of the afferent fibers in the nerve have an inhibitory influence on the contralateral phrenic nucleus, their interruption may activate the latent crossed phrenic pathway. Finally, the experiments will determine if the pathway will continue to function when the denervated hemidiaphragm is reinnervated by a foreign nerve. Surgical, electrophysiological, histochemical, and histological methods will be employed in this research.